This invention relates to an authentication system and more particularly to an authentication system which will be suitable for preventing the abuse of a personal identification unit, such as a magnetic card, an IC card, an optical card and the like prepared for permitting information reference and handling.
An automatic cash dispenser is a typical example of an authentication system which requires a protection scheme to provide security to users. Verification of the bearer of a magnetic card which facilitates access to the cash dispenser is made by checking whether or not a secret number registered to the magnetic card coincides with an input number which is generally manually inputted to the cash dispenser each time a transaction is made. In such a security system, a typical technique for preventing the illegal use of the magnetic card is disclosed, for example, in Japanese Patent Publication No. 29083/1974.
In accordance with the earlier technique, a frequency of errors of coincidence between the secret number recorded on the magnetic card and the manually inputted secret number is recorded, and when the number of times exceeds a predetermined value, that magnetic card is invalidated.
The possibility of illegal use in the prior art technique described above can be reduced by a method such as increasing the number of digits of the secret number, but to do so renders it more difficult for a legal user to remember the number. Therefore, this method has low practical utility. Numbers of four figures are generally employed as the secret numbers of the automatic cash dispensers.
Often times, the secret number may be selectable by a user. It is said that most of the users of the card use the date of their birth or telephone number as the secret number. The magnetic card is subject to illegal use when the card falls into the hands of an illegal user as a result of loss or theft. In such a case, not only the magnetic card, but also the license and name card might fall into the hands of the illegal user. Therefore, he can guess at the prime candidate numbers for the secret number. Since the erroneous input of the secret number is permitted to a predetermined value as described above, the illegal user can make several attempts at the secret number within the range of the predetermined number. In the case such as described above, the illegal user can often be found.